The present invention is directed to liquid developer compositions primarily suitable for electrophotographic imaging processes. More specifically, the present invention is directed to liquid developer compositions comprising a liquid vehicle, a pigment, and a resin selected from the group consisting of polyolefins and halogenated polyolefins. Preferably, the resin is either a poly-.alpha.-olefin or a chlorinated polypropylene.
Liquid developer compositions containing polyolefin resins are known. For example, British Patent 1,436,795 discloses a negatively charged liquid developer for electrophotography or electrostatic printing which comprises a highly insulating carrier liquid and toner particles dispersed therein. Toner particles may comprise a pigment and a binder resin, which resin may comprise polyvinyl chloride, polyvinylidene chloride, vinyl chloride-vinylidene chloride copolymer, chlorinated polypropylene, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate maleic anhydride copolymer, and others. The developer also contains as a negative charge director a copolymer of specified alkene monomers, one of which possesses from about 8 to about 22 carbon atoms. According to the teachings of this patent, the copolymer contains specific functional groups to control the negative charge on the toner particles, provide dispersibility of the particles, and provide fixability of the toner to paper. The toner composition is prepared by first preparing the charge control additive copolymer, followed by mixing the pigment, the resin, and the carrier liquid and dispersing the mixture for two hours in a sand mill, followed by addition of the copolymer to the mixture to form a liquid developer. In addition, U.S. Pat. No. 3,977,983 discloses a similar negatively charged electrophotographic liquid developer wherein the negative charge control agent is a copolymer wherein the amino group thereof is converted into a quaternary ammonium salt or a quaternary ammonium hydroxide. This copolymer is composed of specified alkene monomers which may include long chain alkenes. The toner particles of the developer may also comprise a binder such as chlorinated polyethylene.
Further, U.S. Pat. No. 4,229,513 discloses a negatively charged liquid electrophotographic developer comprising an electrically insulating carrier liquid such as a paraffinic hydrocarbon fraction having stably dispersed therein a halogenated polymer, such as chlorinated polyethylene, halogenated polypropylene, and others, and having dissolved therein a copolymer of a quaternary ammonium salt monomer and a solubilizing monomer, and a copolymer of a polar monomer and a solubilizing monomer. According to the teachings of this patent, the polymeric quaternary salt and the halogenated polymer act in conjunction to confer negative charge and dispersibility on the toner particles. The liquid developers are prepared by first preparing a toner concentrate, which concentrate is prepared by mixing together the stabilizer polymer, a solvent such as a light aromatic hydrocarbon liquid, and pigments, and ballmilling the mixture for several days. The other components are then added and mixed to obtain the concentrate. Alternatively, a viscous solution of the polymers may be placed on chilled compounding rolls and blended with pigments and other additives. The toner concentrate is then dispersed in an electrically insulating carrier liquid to form the liquid developer.
U.S. Pat. Nos. 3,652,269 and 3,738,833 are of collateral interest, showing the use of a chlorinated polyethylene as a binder resin for a photoreceptor.
U.S. Pat. No. 4,880,720, the disclosure of which is totally incorporated herein by reference, discloses an electrophotographic liquid developer composition comprising a liquid vehicle, first toner particles charged to one polarity and comprising a resin and a first pigment, second toner particles charged to a polarity opposite to that of the first toner particles and comprising a resin and a second pigment of a different color from the first pigment, and a charge director. The toner resin particles may include, among other resins, chlorinated olefins such as chlorinated polypropylene, and poly-.alpha.-olefins such as polyoctadecene and polyhexadecene.
Dry electrophotographic developers containing semicrystalline polyolefin resins are disclosed in U.S. Pat. No. 4,952,477 and U.S. Pat. No. 4,990,424, the disclosures of each of which are totally incorporated herein by reference. U.S. Pat. No. 4,952,477 discloses a toner comprising resin particles selected from the group consisting of a semicrystalline polyolefin and copolymers thereof with a melting point of from about 50.degree. C. to about 100.degree. C., and pigment particles. U.S. Pat. No. 4,990,424 discloses a toner composition which comprises a blend of resin particles containing styrene polymers or polyesters and components selected from the group consisting of a semicrystalline polyolefin and copolymers thereof with a melting point of from about 50.degree. C. to about 100.degree. C., and pigment particles. The disclosed toner compositions exhibit lower fusing temperatures and lower fusing energies than many commercially available toners.
Although the known developers are suitable for their intended purposes, a need continues to exist for liquid developers with reduced fusing energies. In addition, there is a need for liquid developers with excellent transfer efficiencies. Further, there is a need for liquid developers containing high concentrations of colored particles. Additionally, a need exists for liquid developers wherein the colored particles have a high pigment to resin ratio. A need also continues to exist for liquid developers that enable the formation of high quality images. Moreover, there is a need for liquid developers that can be prepared rapidly in, for example, about 2 to about 3 hours.